1. Field of the Invention
The present invention relates to a fingerprint reading method of acquiring a fingerprint image of a finger and generating feature information of the fingerprint based on the image. In particular, the present invention relates to a method of using the so-called sweep type fingerprint sensor to successively acquire a series of partial fingerprint images which represent a fingerprint, from a finger which conducts slide operation.
2. Description of the Related Art
Conventionally, a kind of information processing apparatuses such as personal computers or portable telephones equipped with a fingerprint authentication function of ensuring that a user is an owner of the information processing apparatus or a previously authorized user are spread. Especially in a small-sized terminal apparatus represented by a personal digital assistant among the apparatuses of the kind, it is demanded to make the space occupied by a sensor which reads the fingerprint small as far as possible. As a conventional system meeting this demand, a fingerprint collation system using a sweep type fingerprint sensor which successively reads fingerprint images from a finger which slides on a rectangular perception plane having a lateral width equivalent to the width of the finger is known.
Since the sweep type fingerprint sensor in the above-described system continuously reads partial fingerprint images corresponding to a part of a fingerprint, a technical contrivance is needed to obtain information concerning the whole fingerprint from the read partial fingerprint images. As the technique, there is, for example, a technique of reconstructing the whole fingerprint image by successively superposing read partial fingerprint images, and using the whole fingerprint image in registration and collation of personal information, as in techniques in Japanese Patent Application Laid-Open Publication Nos. 10-091769 and 2003-331269 described later. Furthermore, there is a technique of conducting collation processing by comparing continuously obtained partial fingerprint images with a previously registered image without reconstructing the whole fingerprint image as, for example, in a technique in Japanese Patent Application Laid-Open Publication No. 2003-051013 described later.
According to the techniques in Japanese Patent Application Laid-Open Publication Nos. 10-091769 and 2003-331269, it is possible to prevent a missing place from occurring in the whole fingerprint image by superposing the partial fingerprint images. In the above-described technique, however, all partial fingerprint images are read to reconstruct the whole fingerprint image and processing for authentication is started. Therefore, a vast memory space capable of buffering all the partial fingerprint images successively read is needed. Furthermore, there is a disadvantage that the next processing such as extraction of feature information of the fingerprint cannot be started until the whole fingerprint image is completed.
On the other hand, according to the technique disclosed in Japanese Patent Application Laid-Open Publication No. 2003-051013, reconstruction of the whole fingerprint image is unnecessary, and consequently a vast memory space is not needed and the processing time can be shortened. However, the technique lacks important information as to where in the whole fingerprint the feature information of a partial fingerprint image used at the time of collation is located. In principle, there is a problem that it is difficult to implement high-precision collation.